Have we been wrong in our understanding of PAR this whole time??

JoshO

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As the title implies, have we been wrong the whole time about the energy we provide our corals?
I was doing some digging, recently, into journals to better understand what is truly the optimum lighting for Acropora and stumbled across a study which assessed the influence of different Kelvin metal halides on the growth of Acropora Solitaryensis. They studied 5, 10, 15 and 20k temperatures, all with the same PAR value...guess what came out on top? The 20k...the most blue of all the spectrums. I was a little bit baffled by it as we always hear full spectrum is likely to grow corals quicker (anecdotal hobbyist evidence). So I dug a little deeper...here goes.
Light energy is in the form of waves. With the shortest, highest frequency at the UV end of the spectrum and longest lowest at the red end.
PAR is the measurement of the number of photons hitting an area in a given time frame that comes from the range of light which is considered photosynthetically available (I might have worded slightly wrong but hopefully you get the gist). There is no mention of the energy said photons provide, so here is where it gets interesting.
Let's say we've got 200 par of 420nm (blue) light and on another system we have 200 par of 570nm (yellow) light. From the way the hobby has described par these should equate to the same energy levels, correct? Wrong!!
If we go back to what I said earlier about the length and frequency of the light waves then you'll remember that I said blue are shorter and higher frequency. This means that each photon of blue light has more energy than it's friend the yellow photon.
This means that if we base our measurements purely on a par reading, and neglect to factor in spectrum, then we aren't going to be giving our corals the energy we expect!!
 

tbrown

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They've been saying for a while now that PAR measures all available light, not just useful spectrum so yes and no.

The PAR measurements from useful spectrums is really all that matters to our corals, and therefore is the only PAR worth measuring. Additional PAR is only to make it more pleasing to our eyes.
 

Lavey29

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They've been saying for a while now that PAR measures all available light, not just useful spectrum so yes and no.

The PAR measurements from useful spectrums is really all that matters to our corals, and therefore is the only PAR worth measuring. Additional PAR is only to make it more pleasing to our eyes.
Agreed, corals don't need white light it's just for viewing pleasure and to increase par but this increase is not of value to corals
 
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JoshO

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They've been saying for a while now that PAR measures all available light, not just useful spectrum so yes and no.

The PAR measurements from useful spectrums is really all that matters to our corals, and therefore is the only PAR worth measuring. Additional PAR is only to make it more pleasing to our eyes.
Par is a measurement of all visual light including UV. If you measure PAR you're not measuring specific spectrums. 200 par of red light is significantly lower in energy than 200 par of blue light...despite the same par reading
 

Lavey29

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Par is a measurement of all visual light including UV. If you measure PAR you're not measuring specific spectrums. 200 par of red light is significantly lower in energy than 200 par of blue light...despite the same par reading
True especially under water
 
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Agreed, corals don't need white light it's just for viewing pleasure and to increase par but this increase is not of value to corals
"White" light is a blend of all spectrums. So I'd say we have to dig into what you're saying there to understand true meaning. Some of the wavelengths of light in the red area are important to chlorophyll production
 
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True especially under water
So in my original point about are we being misled about spectrum I was saying that I don't think we should be offering PAR as a blanket measurement without first considering the spectral mix of said light
 

Troylee

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Par is a measurement of all visual light including UV. If you measure PAR you're not measuring specific spectrums. 200 par of red light is significantly lower in energy than 200 par of blue light...despite the same par reading
I disagree… 200 par is 200 par, yellow, purple, blue, red etc.. usable, values by coral? Sure it’s different.. let’s not forget about pur lol.. I don’t think we’ll ever know exactly but I prefer and have best results with full spectrum lighting such as metal halides that I run!
 
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I disagree… 200 par is 200 par, yellow, purple, blue, red etc.. usable, values by coral? Sure it’s different.. let’s not forget about pur lol.. I don’t think we’ll ever know exactly but I prefer and have best results with full spectrum lighting such as metal halides that I run!
That's exactly my point. 200 par really isn't just 200 par. It may be the same number of photons, but the energy in each photon is vastly different. If we graded them 1-10 blue would be around 8, whereas red would only be a 3...that's significantly different in terms of energy! So if we are measuring our tanks by alone, one person's 200 par could be significantly lower in energy than another
 
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I disagree… 200 par is 200 par, yellow, purple, blue, red etc.. usable, values by coral? Sure it’s different.. let’s not forget about pur lol.. I don’t think we’ll ever know exactly but I prefer and have best results with full spectrum lighting such as metal halides that I run!
I forgot to ask...which MH are you running? I'd wager there's a significant amount of blue photons in there but the amount of other wavelengths is also high which means total energy output is high. I'm going to guess you're not running 250 par, possibly a fair amount higher?
 

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Par is a measurement of all visual light including UV. If you measure PAR you're not measuring specific spectrums. 200 par of red light is significantly lower in energy than 200 par of blue light...despite the same par reading
Right, I wasn't arguing with you. I'm saying that recently more and more thought has been being put into the measurement of PAR. People measure their PAR with all spectrums turned on and get a reading of 375 but when they turn on blue only they get a PAR of 220 (these are not real measurements...).

Running "full spectrum" with whites on can be anywhere from 6700k (or even less) up to 10,000K or 14,000K which means the PAR is not 100% useful PAR.
 

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It’s also about respiration of the coral. Zooxanthellae are responsible for coral color and general health. Par levels alone are not the cause for coral health and color. As far as what spectrum does what, no idea. Just offering more to the coral color and growth puzzle.





 

Troylee

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That's exactly my point. 200 par really isn't just 200 par. It may be the same number of photons, but the energy in each photon is vastly different. If we graded them 1-10 blue would be around 8, whereas red would only be a 3...that's significantly different in terms of energy! So if we are measuring our tanks by alone, one person's 200 par could be significantly lower in energy than another
Grade them according to what??? We used 6500k haldies for many years there wasn’t any blue leds and very few vho’s to help with a blue spectrum.. corals grew just fine then.. actually grew great.. I’d put a 6500k up against any led today running only blues and it would blow them away.. that’s been my experience anyways. Granted the corals are brown and ugly haha! But they grow like weeds.
 

Troylee

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I forgot to ask...which MH are you running? I'd wager there's a significant amount of blue photons in there but the amount of other wavelengths is also high which means total energy output is high. I'm going to guess you're not running 250 par, possibly a fair amount higher?
I run phoniex 14k it’s got blues for sure.. my par is 1000 under the water line and around 400-600 on rocks and 250 in the sand.
 
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JoshO

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Right, I wasn't arguing with you. I'm saying that recently more and more thought has been being put into the measurement of PAR. People measure their PAR with all spectrums turned on and get a reading of 375 but when they turn on blue only they get a PAR of 220 (these are not real measurements...).

Running "full spectrum" with whites on can be anywhere from 6700k (or even less) up to 10,000K or 14,000K which means the PAR is not 100% useful PAR.
I know, it's a discussion . Your point here is exactly what I'm implying needs to be done. We need to measure our par by only measuring the blue end of the spectrum (and possibly a very small amount of red, but that's debatable with how important blue is. I'm currently reading a study on red repression). Then if we leave the blues alone and add in the whites for our own visual pleasure we'll have a much more effective lighting set up.
For clarification this relates to LEDs more than other light sources. A 6500k metal halide will have all the blue necessary most likely, it just has a lot of the other wavelengths too. The par this gives out will be significantly high than day a 20000k MH I'd assume
 
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Grade them according to what??? We used 6500k haldies for many years there wasn’t any blue leds and very few vho’s to help with a blue spectrum.. corals grew just fine then.. actually grew great.. I’d put a 6500k up against any led today running only blues and it would blow them away.. that’s been my experience anyways. Granted the corals are brown and ugly haha! But they grow like weeds.
Would I be right to assume your par under that 6500k MH was much higher than say a 20000k?
In the case of the 6500 it has the same amount of blue photons as the 20000, which means the energy provided is great. When we get the 20000 it means the wavelengths of red, yellow green etc have been reduced, but the blue volume remains at a constant.
With LEDs it's possible to remove blue to encourage a more "full spectrum" look under the same par as all blues. This is where I think so many are falling down.
 
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